[rrd-users] rrdtool - features ... 2nd y-axis

Tobias Oetiker tobi at oetiker.ch
Sun Jun 1 00:57:30 CEST 2008

Hi Karl,

> @Tobias:
> can you tell me if it's possible to use such a wrapper function? That means there
> should be (at best) only one single point in the code that does store & retrieve?

as I said before the problem is not a wrapper function or anything.
The problem is that in all likely hood you are not able to collect
data exactly every 300s or so. Meaning, that rrdtool will have to
re-aligne/re-sample the data or you will get serious distortions in
the values you store.

If you now store everything as integer, this resampling process
will loose precision which is realy not something you would want
todo to your data.

So if you insist on storeing your data as integers, you would have
3 options:

a) devise a magical way that enables you to collect all data at
   exactly time % step == 0

b) lie about the data collection time, and fill in the data that
   you collected at time % step == x at time % step == 0

c) use a  generic (SQL) database where you can store the data you
   collected as well as the time you did collect the data.

The whole exercise though makes little sense. The point is not to
keep the data 'pure'. The interesting thing is to select a samping
interval that is correct for the rate of change in the data you are

hope this helps

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten
http://it.oetiker.ch tobi at oetiker.ch ++41 62 213 9902

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